Landing Gear Handle some hands-on mechanical work ...

Introduction

Robert, "Dunk" on Viperpit, offers a Landing Gear Box as a "Do-It-Yourself" kit.
He molds all major parts, so the only thing you have to do is the assembly ...

Thanks Goodness, Dunk posted a lot of pictures on Viperpits. I looked for quite some time (a lot of times in fact) at those pictures.
Slowly the construction became clear to me. I wanted to be 100% sure to build it correctly, because you need to drill a few holes.

Inventory

When you order the Landing Gear Box kit from Dunk, this is what you get (picture from Dunk himself). gearbox parts

As you can see, there is still a lot of work that needs to be done, and there are several parts not included in the kit. You have to find these parts yourself. However, the most important parts that determine the great visual appearance of the Landing Gear are in the kit: the handle itself, the protruding case for the release button on the handle, the "crystal" which goes on top of the handle, and finally the yellow-ish manual release button.
Other parts that make this construction complete are the two (top and bottom) walls of the box, the left side mounting plate, a support bracket and arm that gives the handle the "lock into place" feeling.
So, which additional parts do you need to complete the Landing Gear Box? Here is a short list.

some small self-threading screws, normally used for wooden parts (diameter 2 to 3 mm, length 12 and 15 mm)
small round momentary push-button that fits in the protruding case for the PERMISSION button on the handle
small micro-switch, to detect the movement of the handle going from one to the other position
two small micro-switches to detect the "UP" position of the Landing Gear handle
micro-switch to detect the activation (push down) of the yellow manual release button
small (not too strong) spring, to give the handle its "lock into place" feeling
larger spring (somewhat stronger) to keep the yellow manual release button up (and return after pushing)
bolt, diameter approx 8 mm, lenght approx 40 mm, to guide the yellow manual release button
solenoid, lever, and a round rod to lock the Landing Gear handle, preventing operation when not allowed!

But, above all, you need patience if you want to finish with a great looking Landing Gear handle!

Assembly of the Gear handle

There are a lot of pictures on Viperpits, so I will only describe how I have built the Landing Gear handle, with just a few pictures.
First, look carefully at the pictures (I can not say this enough!). Drill a hole from the top, where the cup will come for the crystal, straight down into the handle using a small 2 mm drill. Don't worry that the hole will not be deep enough. What is important here is that you drill down straight, keeping the drill centered. The small hole is a guide for the next drill which has a diameter of 3 mm. See, this goes easy and you can drill the hole a little deeper into the handle. Finally, use a 4 mm drill to get a hole that will be large enough to guide 4 wires. With the drill just a short part clamped in the tool you can drill the hole almost down to the base part of the handle.
Now, repeat the procedure, going from a small drill to a larger drill, from the opposite side. Draw a line on the base of the handle as a reference guide how the drill will have to go inside to meet up with the already drilled hole down the shaft of the handle. Make sure that the hole for the wires keeps clear from the pivot hole in the base of the handle.
The yellow/white and the pink wire give you an idea how the hole throught the shaft must be drilled.

The yellow/white wire is a "fishing" wire to pull the 2 wires from the crystal down the hole through the shaft. Likewise, the pink wire is the "fishing" wire for the 2 wires from the release push-button. The metal rod (vertical in the picture) is just used to let the handle rest on it, so that the crystal cup holder is free (it was just an hour before glued!). More about this metal rod when I get to the description of the locking solenoid ...

Next step is the mounting of the crystal holding cup and the protruding holder for the release push-button. You need 3 screws, diameter between 2 and 3 mm. Two screws have a length of 15 mm, the third screw has a length of approx 12 mm.

One long and one short screw are used to mount the crystal holding cup onto the handle. Make sure you hold the cup correctly oriented on the end of the handle and mark the holes to be drilled. Drill the holes using a 2 mm drill.
Make sure that the drill does not drill a hole throught handle, so check the drilled depth regularly!
Mount the crystal holding cup with the two screws, but do not tighten the screws. It is just a check that everything fits, and that the threading is made in the handle.

Hold the protruding holder for the release push-button on the handle, and mark the hole to be drilled in the holder. Again, make sure not to drill the hole through the holder! Finally, enlarge the hole for the holder in the handle at the opposite side to have the screw sunken into the hole.
(In the picture, you can see that I goofed up, and enlarged the hole at the wrong side. Luckily for me, it was not drilled too deep, so I could enlarge the hole at the opposite side just deep enough).
After you found a round push-button that will fit in the protruding holder for the release push-button, solder two thin wires to the contacts and put some heat-shrinking tube around the solder pins (the wires from the crystal will run over them). Check that the wires with the push-button all fit when you hold the protruding holder at the correct position on the handle. Mount the screw, but do not tighten the screw. Again, it is just a check that everything fits, and that the threading is made in the protruding holder.

Use some sandpaper to smooth all edges of the handle, the crystal holding cup and the protruding holder for the release push-button. You will have to sand them more after they are mounted onto the handle, but with the first sanding, especially of the handle, you can keep the sanding to a minimum after the two parts are mounted on the handle.

Put a piece of shrink tube in the top of the handle that fits nicely in the drilled hole and the hole in the crystal holding cup. This will prevent glue going into these holes which will make it very difficult to get the wires through later on ...
Apply some epoxy (2-component) glue on the end of the handle and then put the crystal holding cup onto the handle. Mount the two screws to keep the cup in its place. Do not worry about the excess glue around the corners; it is a good thing that some excess glue is there. After the glue is hardened you can sand it down to some nice looking curves.
Check once again that the push-button with the wires fits, and notice how the push-button sits in the protruding holder. Use a little epoxy glue to glue the push-button in its final location. Take a break ...!

After the glue for the crystal holding cup (and the push-button) has hardened for some hours (read the instructions of the glue you use ...!), you can repeat the procedure to mount the protruding holder with the push-button onto the handle.
First, guide the two wires of the push-button through the handle. I soldered the two wires together on the pink "fishing" wire and gently pulled the pink wire through the handle until the push-button wires appear at the hole in the base. Just make sure that the yellow/white wire stays where it is, you need that wire to pull the wires of the crystal through the handle!
Apply just a little epoxy (2-component) glue on the flat surfaces of the protruding holder and then put the holder onto the handle (do not use too much glue; the excess glue does not only go to the outside, which is OK, but also goes inside and could glue the "fishing" wire for the wires of the crystal!). Mount the screw to keep the holder in its place. Apply some additional glue on around the holder at the outside! Again, after the glue is hardened it will be sanded down to some nice looking curves. Finally, use some glue to fill up the hole of the sunken screw at the opposite side.

Landing Gear handle ready to be sanded and the spray-painted

Assembly of the box

The assembly of the box is a "process". First, try every part (without glue or screws) to see how everything fits and to get acquainted with the construction. I needed a few hours in total to get a clear grasp of it all. Remember, you only have those parts just once, so unless you want to buy a second kit, make sure to do everything the first time right! It also helps to see which additional parts you must get, such as springs and switches. Some holes are already drilled by Dunk, you have to drill the other mounting holes.
The bolt that goes from the left side mounting plate through the hole in the handle, then through the support bracket, is very close to the top lid. The nut that secures the bolt and the handle must be filed at one side, as visible in the pictures from Dunk ... I took another approach. With a dremel I created space for the nut in the rear side of the top lid. After some "toy-ing", I put the top lid and left side mounting plate together with glue and two screws. On the parts picture from Dunk, at the top of this page, the top lid is in the bottom left corner, and the left side mounting plate of the box is in the top left corner.

To continue the assembly of the other parts, I mounted the bottom plate of the box preliminary with the two screws only no glue!. Now you can create a construction for the yellow release button. No guide is supplied, so you are on your own how to construct it. I can only show how I did it. Its operation was not clear to me at first. "Rabbit" and "Dunk" on Viperpits explained it to me. In the real Landing Gear Box, the yellow release button mechanically releases the handle for emergency situations. In "our" Landing Gear Box, the yellow release button only activates a micro-switch, which in turn activates a solenoid. The solenoid pulls a locking pin which obstructs the movement of the handle, thus simulating the "mechanical" release.
LG box release button

So, in "our" box the yellow release button only needs to move some 5 mm. If the button is not pressed, a spring makes sure that the button is in the "upward" position. You can feel the spring clearly if you push the button down and if you let go, the yellow button returns to its "upward" position.
First, the hole in the top lid for the yellow release button is a bit large. That causes the button to have too much free movement perpendicular to the desired up/down movement of the button. I solved this by a piece of heat-shrink tube.
At the opposite side of the box I mounted a 40 mm long M8 threaded screw-rod on the bottom plate, secured by nuts at both sides. The length of the screw-rod is such that when the yellow button is completely "in" it does not touch the M8 screw (a few mm spacing remains). The part of the screw-rod that is not used by the nuts and the metal ring is covered by a piece of heat-shrink tube to get a smooth surface.
It took some time to find the missing piece: a "tube" that fits snug on the end of the yellow release button, but its inside diameter is just a little more than the diameter of the M8 screw-rod with the heat-shrinked tube. Don't laugh ... I used the top cover of a fineliner! It is the blue part in the middle.

The assembly order is as follows. First, put a ring on the screw-rod against the heat-shrinked tube, followed by the nut. Put the screw-rod in the bottom plate and secure the screw-rod with the M8 nut at the outside. Slide the fineliner top cover over the heat-shrinked tube M8 end, and then slide the sping over the fineliner top cover. Put the yellow release button (with the heat-shrinked tube in place) through the top lid and, while sliding the button in, put an M10 nut on the shaft of the release button. Between the M10 nut and the top lid is a clamp. This clamp limits the length that the yellow release button extends from the top lid, and together with the M10 nut, gives some pre-tension to the spring. If the spring that you use is shorter, you might add another M10 nut, or use more rings on the screw-rod. The clamp is nothing more than two M3 screws and nuts and two metal pieces from a household appliance power plug: the part that fastens the cable to the socket body!
If you are satisfied with the (working) mechanical construction, disassemble it for now to do some more work on the box itself.

Next item to assemble is the resistor verticle. It is a small "lever" constructed with the part in the top row of 3 parts in the picture that shows all the parts of the kit. It is left of the large black plate. On Viperpits in the "Landing Gear" thread you can see how Dunk constructed the lever. The push-button on the lever closes when the Landing Gear handle moves from one to the other position. Initially, I also made a small aluminum bracket to hold the push-button. However, due to the movement of the lever driven by the Landing Gear handle, the push-button has to go to its maximum movement without any free movement tolerance. I did not like that "error-margin-free" construction. My solution uses a small micro-switch. When you read the specifications of a micro-switch, you see that the length of travel of the arm on the micro-switch is several mm after the contacts of the micro-switch are closed. Those extra mm's are the tolerance we want!


Resistor verticle with micro-switch installed

To give the Landing Gear handle its "lock into place" feeling, the lever must push against the handle. This is realised by a small spring between the resistor and the bottom plate. Drill a hole in the resistor arm with a diameter a bit larger than the diameter of the spring. The depth of the hole needs to be just a few mm, partly depending on the length of the spring you use. The tension of the spring is not too large; it just needs to give that "lock into place" feeling. Dunk already made a "hole" in the bottom plate to keep the spring in its location. However, the spring that I used has a rather small diameter, so I installed an M2 screw to keep the spring where it should be.


Landing Gear box with painted handle installed (click on image for larger view)

The stand-offs at the left are mounted on the bottom plate (left in the picture) with sunken screws from inside the box. On the stand-offs I will mount the D-SUB male connector. The picture at the right side has the locking pin in the support bracket to check whether the locking pin will actually lock the handle in the "UP" and in the "DOWN" position.

Electric connections to the box

There are a few wires from the Landing Gear Box, each electrical component has 2 wires: the yellow push-button micro-switch, the push-button in the handle, the crystal, the micro-switch that detects the movement of the handle and the solenoid. That is 10 wires. As I do not like wires from a box, I mounted a 9-pin D-SUB male connector on the bottom plate. 9 pins are enough, because the push-buttons of the handle and the yellow button can be wired with one connection in common as both only activate the solenoid. And even if the push-buttons are wired to inputs (Key-64 switch matrix) and detected by software, which in turn will activate the solenoid, 9 pins are still sufficient. If I really need that "missing pin", I can substitute the 9-pin D-SUB with a 15-pin high-density D-SUB which has the same dimensions.

Update
I read the "Real Landing Gear Box" from "Nigel" on Viperpit. It describes how the real Landing Gear operates, especially the operation of the PERMISSION button on the handle, the yellow release button and the locking solenoid. I decided that I want to mimic the real behavior as much as possible, given the available box. As a result, I added one more micro-switch that detects the "UP" position of the handle. The two small micro-switches can be mounted on top of each other, and luckily for me, the width of the base of the handle is such that it will push the levers of both micro-switches. Why two micro-switches? Well, one is needed to inform the software of the position of the handle (connecting a switch "position" in a key matrix), and the other micro-switch is used in the electrical circuit that operates/locks out the solenoid. As a result, the 9-pin D-SUB will not have sufficient pins, so I used a 15-pin high-density D-SUB connector. It has sufficient pins to make the "Normal Open" (NO) and "Normal Closed" (NC) pins of the micro-switches available for connection, except for the micro-switch that is wired in a matrix for the software. Of that micro-switch I am sure I will only need the "NO" contact. By having the "NO" and "NC" contacts available I have maximum flexibility in the design of the locking solenoid functionality.

The "finale": Landing Gear handle lock mechanism

There real Landing Gear handle can not be moved while the F-16 is on the ground (... makes sense). And while in the air, the handle can not be moved "by accident" from "UP" to "DOWN". At high speed that would damage the landing gear. So, there is a mechanism that physically blocks the movement of the handle. In this replica Landing Gear box the blocking action is realised by a pin that can be lifted by activating a solenoid. The pin blocks the movement of the resistor verticle, thus blocking the movement of the Landing Gear handle. The solenoid must be activated to unlock the handle.
The (metal) pin to block the resistor verticle is from the paper transport mechanism of an old (defective) matrix printer. That paper transport mechanism has several useful parts. The metal rod rolls smoothly in brass bushings so keep those too. I used a few of the toothed gears from the paper transport mechanism for the construction of the wet compass rose control with a servo and a magnet. I saw the rod to the appropriate length, and at 23 mm from the end which will lock the resistor verticle I drilled a 2,5 mm hole through the rod. By sharp bending of a paper clip you have the small round "eye" at one side of the rod, and the hole is large enough to slide both ends of the paper clip through the rod. Bend both ends of the paper clip away from each other, around the surface of the rod. Cut off the excess length. You do not need much paper clip outside the rod if you drilled the hole in the support block just a little larger than the diameter of the rod. (The support block is the rectangular piece above the crystal and the yellow release button in the parts picture at the top).

To move the locking pin up and down a lever is attached to the pin. A spring mounted to the lever makes sure that the pin is pulled to the "down" position, thus locking the Landing Gear handle when the gear system is not active. At the other side of the lever is the core of a solenoid attached. When the solenoid is activated the core is pulled into the solenoid. As a result the lever will lift the locking pin, thus releasing the Landing Gear handle. The lever has its pivot point on a small piece of L-shape aluminum profile which is mounted to the front and rear side walls of the box.
The L-shaped aluminum profile (both sides are just 10 mm) is positioned such that between the profile and the plastic support bar some space is available to mount a spring.

There is no space to install the solenoid inside the box, so it has to be mounted externally. There are two possible positions: at the rear side of the box or on the top side of the box. I have chosen for the top side of the box, because the length of the lever arm could be a bit longer. However, keep in mind that near that location (above the Landing Gear box) is the body of the "HOOK" switch of the Landing Gear panel. So, do not mount the solenoid too close to the front!
The spring that forces the pin to the locking position is either a "pushing" type when installed at the side of the solenoid, or a "pulling" type when installed near the pin. The latter is easier (for me), so I attached a spring to the lever near the pin and the other end of the spring is conveniently attached to the plastic support bar.
To mount the solenoid the way I wanted, I used an L-shaped piece of aluminum (length of both "legs" is 20 mm). The solenoid is mounted on one leg, the other leg mounts the aluminum piece to the black plastic wall at the top.


Landing Gear box completely finished -- ready for installation (click on image for larger view)

Electrical interface

On the Landing Gear handle is small push-button called "permission", and the "crystal" with an LED inside it. The big yellow Manual Release button is on the Landing Gear box. In the real Landing Gear box that button mechanically unlocks the Landing Gear handle. In this construction that would be too difficult to realize, so the Manual Release button simply activates the solenoid at all times (provided the electrical power is connected). Inside the Landing Gear box are a few micro-switches to detect the position of the handle. Some micro-switches are used to let the software knwo the handle position, other micro-switches are used to realize the electrical landing gear up/down functionality in combination with the locking solenoid.

I discovered too late (more than a year ...) that the "permission" button that I used in the handle was not of the "make contact" type, but it was a "break contact" type when pushed. I originally intended that, when the "permisssion" button is pushed, the unlocking solenoid is activated. That is not possible with the break contact, so some solution had to be found.
Landing Gear circuitry

The blue numbers in the schematic diagram refer to the pins I allocated on a HD-15 pin sub-D connector. As you can see, when the Release Button is pressed the micro-switch (wired to pins 1-2-3) will always activate the solenoid.

Plane is in the air
The Gear Down handle is in the "up" position, and the WOW signal (Weight On Wheels) supplied from the software is active. The solenoid is not activated, but can be activated by pushing the "permission" button so that the Gear Down handle can be moved to the "down" position (just before landing on the runway). As long as the "permission" push-button is not pressed, because the button is a break contact, the gate of the MOSFET is connected to GND, thus is not in the conducting state. When the button is pressed the MOSFET will conduct and the solenoid is activated. Now you can move the Gear Down handle to the "down" position.

Plane is landing
The Gear Down handle is in the "down" position. As the software has the WOW signal active, the solenoid remains activated. After the plane has landed on the runway the software disables the WOW signal. The solenois is no longer activated and the Gear Down handle is locked in the "down" position.

Taxying runway, ready to take off
When the plane is in the air the software enables the WOW signal. The solenoid is activated and the Gear Down handle can be moved to the "up" position. When the Gear Down handle is in the "up" position the solenoi is no longer activated. The WOW signal can be enabled again by the software.

Of course, the on and off switching of the LED in the "crystal" on top of the Gear Down handle is also controlled by the software. If your "permission" push-button is of the "make contact" type, change the 100k resistor to 1M, remove the 120k resistor, and connect the push-button instead of the 120k resistor.
In hindsight, it is a good idea to use MOSFETs (or relays) to activate/deactivate the solenoid. The solenoid draws some 0.7 Amps at 18V and for long-life of the small "permission" button that would be a lot of switching current ...

This is a sketch of how I plan to build the Gear handle "interface". At the top side are the connections that connect to the high-density 15-pin connector on the Landing Gear box. At the bottom side are the connections to the hardware interface (PHCC switch matrix and PHCC digital outputs).

And here is the final result. It works nicely!